A site-directed CO2 detection method for monitoring the spoilage of stored grains by insects and fungi in Chinese horizontal warehouses

Detection of CO2 concentration in grain bulk is an efficient way to monitor insect and microbial activities. To develop a practical CO2 detection system suitable for Chinese horizontal warehouses, multiple fixed sampling points in the grain bulk were used to determine the factors associated with CO2 detection in grain warehouses containing over 4000 tonnes of wheat or corn. CO2 detection was significantly (P < 0.01) affected by pipe size, and pipes that were less than 30-m in length (2-mm internal diameter × 4-mm external diameter) were the most suitable for CO2 detection in 6-m-high grain bulks. The gas flow needed be set to the maximum rate of the CO2 sensor in order to minimize detection time. The CO2 produced by grain respiration was relatively low, and the activity of insect and mould significantly affected the CO2 concentration in the bulk. Spatial changes in CO2 concentration around artificial hot spots were sensitively detected within 2 m of the hot spot in both the horizontal (P < 0.05) and downward directions (P < 0.01), as well as within 1 m of the hot spot in the upward direction. Therefore, the multiple fixed-point CO2 detection method has great potential as an indicator of grain spoilage in Chinese horizontal warehouses.